SOMETHING WAS WRONG with Kai Markram. At five days old, he seemed like an unusually alert baby, picking his head up and looking around long before his sisters had done. By the time he could walk, he was always in motion and required constant attention just to ensure his safety.

“He was super active, batteries running nonstop,” says his sister, Kali. And it wasn’t just boyish energy: When his parents tried to set limits, there were tantrums—not just the usual kicking and screaming, but biting and spitting, with a disproportionate and uncontrollable ferocity; and not just at age two, but at three, four, five and beyond. Kai was also socially odd: Sometimes he was withdrawn, but at other times he would dash up to strangers and hug them.

Things only got more bizarre over time. No one in the Markram family can forget the 1999 trip to India, when they joined a crowd gathered around a snake charmer. Without warning, Kai, who was five at the time, darted out and tapped the deadly cobra on its head.